That runtime path doesn't look right to me. When I try to run set runtimepath^=somepathonmysystem vim gives me an unknown option error. Maybe you meant to type $VIMRUNTIME which you shouldn't need to do just to configure ctrlP.
Usually the problem with vim on windows is it gets its cwd from the shortcut launcher if you haven't set that. You may need to be conscious of what your current working directory is. cd to e:\workspace and try and it should work without needing special configuration.
Instead of setting the runtimepath in the vimrc on windows, I right-click the shortcut-icon on the taskbar, go to its properties, and there's a field in the properties where you can set the path that vim starts up in, so I set that to my home folder and avoid confusion.
I hope this helps! I tried to post some images but not enough rep.
EDIT: Sweet! I can post images now.
Also, note that you can enter a shortcut (hotkey) for your shortcut (link).
Control + Shift + N in this case. (Just type N into the box.)
Notes on using this method of changing where the shortcut starts up in: Don't go overboard. At first I was like ooh I'll have one to launch vim here and one to launch vim here and then ... well anyway I DO suggest windows vim users might want to set this on the launcher but I DON'T suggest making a ton of different launcher shortcuts for the same program just starting in different places. It's a slippery slope.